We are using external database (Oracle) for enrolments. When launcing enrol/database/enrol_database_sync.php (from command line), few error messages appeared that object does not contain specified fields.
Example -
"PHP Notice: Undefined property: stdClass::$kkods in /home/moodle/moodle/enrol/database/enrol.php on line 260"
"PHP Notice: Undefined property: stdClass::$login in /home/moodle/moodle/enrol/database/enrol.php on line 317"

We have added functionality to script enrol/database/enrol.php. Lines of code in original Moodle v1.9 enrol/database/enrol.php are 225, 282 respectively.
$extcourse = $extcourse_obj->{$CFG->enrol_remotecoursefield}; - #225
array_push($extenrolments, $crs_obj->{$CFG->enrol_remoteuserfield}); - #282

These errors disappeared and script worked fine when on enrollments administration page Courses->Enrolments->External Database (edit) (admin/enrol_config.php?enrol=database) remote database fields "enrol_remotecoursefield" and "enrol_remoteuserfield" were saved in upper case.

There was no need to save remote database fields in v1.8 in uppercase. Possibly it this bug deals with new version of adodb database drivers in Moodle v1.9 comparing with drivers used in Moodle v1.8.